An analytical approach for electrogenerated chemiluminescence based on the electronic states of light emitting materials

Electrogenerated chemiluminescence can be seen because of radiative transitions from excited states, which are formed through homogeneous electron transfer between the electrochemically generated oxidized and reduced form of a light-emitting material. Therefore, photophysical and electrochemical properties with homogeneous electron transfer processes can affect the ECL properties. Although the ECL spectra and intensities (efficiencies) are the main concern as the ECL properties, by analyzing the ECL properties while considering the photophysical and electrochemical properties with the electronic states, it is possible to understand the ECL properties deeply. Here the ECL properties of some light-emitting molecules, such as thermally activated delayed fluorescent molecules, a borondipyrromethene derivative, and liquid fluorescent molecules, are summarized along with their electronic states. The electronic states of Ru(bpy)₃ ²⁺ and its oxidized and reduced forms were estimated with density functional theory calculations to reveal the relationship between the electronic state and the redox behavior of the metal center and ligands. The kinetics for the formation of the lowest excited singlet and triplet states were estimated with the Marcus theory by considering the diffusion of the electrogenerated species. Moreover, simulating the ECL behavior with a coreactant, tripropylamine, based on a finite element method, was described.